Heart disease is the leading cause of death for both men and women. More than five million Americans have heart failure and the number is still on the rise. Blood pumps are effective in treating heart failure, but can also cause side effects such as blood cell damage (hemolysis) and blood cell clotting (thrombosis).
Hemolysis and thrombosis can be primarily attributed to high shear stress and flow stagnation inside the blood pump. Early generation of blood pumps were known for causing thrombosis due to shaft seals or contact bearings between the rotating components such as rotors and the stationary components such as stators. Later hydrodynamic bearings eliminated the direct contact between the rotor and the stator by using blood as the lubricant. However, high shear stress created inside thin films in the later pumps is a major source of hemolysis. More recently developed blood pumps include magnetic bearings in which magnetic forces suspend the rotor in the blood with large gaps between the rotor and the stator and thus can greatly reduce the shear stress. However the more recent blood pump designs with magnetic bearings include extra components, double-shrouded impellers and with magnets embedded inside the shroud. The extra components and shrouded impellers can add substantial weight and size to this type of blood pump.